The invention relates to the field of transistors, and in particular the fabrication of near room temperature processed high-K and low dielectric loss transparent transistor circuits using transparent high-K gate insulators.
Organic light emitting diodes (OLEDs) are of great interest due to their potential application in flat panel displays. More significantly, the hydrogenated amorphous silicon (a-Si:H) active matrix is a very promising technology for back-plane electronics for a new generation of displays based on OLEDs on transparent glass substrates. Amorphous Si has an advantage of lower processing costs despite its lower mobility compared to poly-Si.
Although there have been successful demonstrations of flexible OLED's fabricated on plastic substrates, the fabrication of a-Si transparent flexible transistor (TFT) on plastics has proven difficult due to mechanical and chemical instabilities of such substrates at the processing temperatures typically needed for a-Si transparent flexible transistor TFT (˜300° C.). For Active Matrix OLEDS (AMOLED) applications, SiNx gate dielectrics are commonly used for TFT fabrication. However the low dielectric constant of SiNx requires higher driver voltages, not compatible with battery powered wearable and portable devices. Currently, OLEDs can be made to emit light from bottom and top surfaces.
AMOLED displays have a transistor driver supplying a constant current source at each pixel with one switching TFT to program. Hence, AMOLED display pixels need a minimum of two TFTs to control the drive current. The transistor is used to separate the effect of the data line voltage and the address line voltage on the voltage across the OLED material. Each pixel with p-channel transistor is programmed to provide a constant current. Amorphous silicon and polycrystalline silicon are commonly used for AMOLEDs. Both of these materials are compatible with large area glass substrate processes, however, poly-Si technology is expensive compared to amorphous-Si technology even though poly-Si has much higher mobility. In terms of process temperature, amorphous-Si has an advantage. OLED display technology offers better viewing angles, more resolution and less power consumption than traditional LCD displays.